A known procedure for determining the temperature of a medium, such as soil, over a chosen period of time is to read and record individual temperatures at more or less regular intervals over the chosen time and then to calculate the arithmetic mean of the recorded temperatures. The readings may be made directly from thermometers or thermocouples placed in the medium. The accuracy of the calculated mean is related to the number of recordings made, the amplitude and frequency of the natural temperature variation and the amount of disturbance caused to the natural temperature regime by the device employed and/or by the act of making the reading. The devices employed are also generally in an exposed position and consequently open to interference by animals. Since many readings and recordings are usually necessary, labour and administrative costs are high and the overall operation is expensive. Further, quite often the sites at which the devices are placed are in remote areas which causes additional labour charges and other difficulties in obtaining regular readings.
It is an object of this invention to provide a cumulative record of a medium's temperature history over a period of time without the requirement for making numerous measurements over a period.
It is a further object to reduce the disturbance to the medium during the period.
A still further object is to effect the temperature recording at a diminished cost.